The present invention relates to a non-reciprocal circuit device such as a circulator, an isolator, etc., particularly to a miniaturized, low-loss, highly reliable non-reciprocal circuit device and wireless communications equipment such as a cellular phone comprising such a non-reciprocal circuit device.
Non-reciprocal circuit devices such as circulators, isolators, etc. have characteristics of transmitting a signal to only a particular direction while preventing the signal from being transmitted in the opposite direction, and thus are indispensable parts for transmission circuits of microwave transmission equipment for automobile phones, etc. In such applications, the non-reciprocal circuit devices are required to be miniaturized and reduced in loss. A non-reciprocal circuit device, for instance, an isolator, comprises a magnetic body such as a garnet member, etc., three central conductors disposed on the magnetic body such as a garnet member while overlapping at a 120xc2x0 interval with electric insulation from each other, a permanent magnet for applying a DC magnetic field to the magnetic body, matching capacitors and a metal case serving as a magnetic yoke and containing these parts.
FIG. 15 shows an isolator, one example of the conventional non-reciprocal circuit devices, disclosed in Japanese Patent Laid-Open No. 11-205011. This isolator comprises a box-shaped resin-conductor composite base 96 disposed on a lower case 92, the resin-conductor composite base 96 having recesses 100 for respectively receiving a central conductor assembly 4 comprising three central conductors 11a-11c disposed on a garnet member 12 with electric insulation from each other, matching capacitors constituted by three flat capacitors 94a-94c, and a chip resistor 95. Each recess 100 of the resin-conductor composite base 96 is defined by an insulating thermoplastic resin partition 101 for positioning each part. Formed at the bottom of the recess 100 is a ground electrode 102 (indicated by hatching) for connecting the central conductor assembly 4 and the capacitors 94a-94c to a ground. Each central conductor 11a-11c has one end connected to an electrode of each capacitor 94a-94c and the other end connected to a ground electrode 102 on the resin-conductor composite base 96. Each flat capacitor 94a-94c has two opposing electrodes, one connected to each central conductor 11a-11c, and the other connected to the ground conductor 102. A resistor 95 is connected to the flat capacitor 94c in parallel. A permanent magnet 93 for applying a DC magnetic field to the central conductor assembly 4 is disposed in an upper case 91, which is combined with the lower case 92 to constitute an isolator.
Each of the upper case 91 and the lower case 92 is formed by an iron-based magnetic sheet such as SPCC (cold-rolled steel sheet) plated with silver for functioning as a magnetic yoke constituting a magnetic circuit for applying a magnetic force of the permanent magnet 93 to the central conductor assembly 4. A conductor plate constituting the ground electrode 102 in the resin-conductor composite base 96 is bent to integrally have ground terminals 97b, 97c exposing from the lower and side surfaces of the resin-conductor composite base, exposed portions of the conductor plate being plated with silver. The resin-conductor composite base 96 is provided on a lower surface with an input/output terminal 97a and ground terminals 97b, 97c. Though not shown, the opposite surface of the resin-conductor composite base is also provided with an input/output terminal 97a and ground terminals 97b, 97c. Accordingly, each of the two central conductors 11a, 11b has one end connected to the input/output terminal 97a via the flat capacitor 94a, 94b, and the other end connected to the ground terminal 97b, 97c via the ground electrode 102. The remaining one central conductor 11c is connected to the ground terminal 102 for termination via the capacitor 94c and the resistor 95.
FIG. 16 shows an isolator, another example of the conventional non-reciprocal circuit devices, disclosed in Japanese Patent Laid-Open No. 9-55607. This isolator has matching capacitors formed inside a laminate module 105 disposed on a lower case 92, and the laminate module 105 having a center opening 110 for receiving a garnet member 12 and a central conductor assembly 4 constituted by three central conductors 11a-11c, one end of each of three central conductors 11a-11c being connected to a capacitor 106a-106c printed on an upper surface of the laminate module 105. A capacitor 106c connected to one central conductor 11c is electrically connected to a resistor 107 in parallel. The other ends of three central conductors 11a-11c are directly connected to the lower case 92 without using a ground plate. A permanent magnet 93 for applying a DC magnetic field to the central conductor assembly 4 is disposed in the upper case 91, which is assembled to the lower case 92 to constitute an isolator.
Formed in the laminate module 105 are three matching capacitors in single or multi-layers, and electrodes of the matching capacitors are connected to each other through via-electrodes in the laminate module 105, or external terminals of an input/output terminal 108a and ground terminals 108b, 108c printed on side surfaces of the laminate module 105 as in this example. The laminate module 105 has projections 112 on both sides of a lower surface thereof, onto which an input/output terminal and ground terminals (not shown) are mounted, and a recess 114 between the two projections 112 is formed with an electrode (not shown) for connecting to the lower case, whereby the ground terminals are connected to the lower case-connecting electrodes. The other ends of the central conductors 11a-11c, namely the side of the central conductors 11a-11c connected to the lower case 92, are connected to a ground in a circuit board via the lower case 92 and the lower case-connecting electrode and the ground terminals 108b, 108c of the laminate module 105.
The market of microwave communications equipments such as cellular phones, etc. has dramatically been expanding recently, accompanied by the rapid miniaturization of cellular phones. Arising with the miniaturization of cellular phones is a strong demand to miniaturization of such parts as isolators, etc., and particularly the isolators are most strongly demanded to be small in size and low in loss. If the conventional isolator disclosed in Japanese Patent Laid-Open No. 11-205011 were to be miniaturized, then parts such as a garnet member 12, flat capacitors 94a-94c, etc. would have to be miniaturized. The capacitance of a capacitor is expressed by
C=xcex5rxc2x7xcex5oxc2x7S/dxe2x80x83xe2x80x83(1) 
wherein C is a capacitance of a capacitor, xcex5r is a specific dielectric constant of a dielectric body, xcex5o is a dielectric constant of vacuum, S is an area of an electrode, and d is a thickness of a dielectric body between the electrodes.
The formula (1) indicates that to keep the same level of capacitance even when the electrode area S is reduced by the miniaturization of the matching capacitor, it is necessary to use a dielectric body with a large specific dielectric constant xcex5r or to reduce the thickness d of a dielectric body between the electrodes. However, dielectric bodies having large specific dielectric constants generally tend to have large dielectric loss, resulting in the loss characteristics of capacitors and thus increase in the loss of isolators.
When a dielectric body disposed between the electrodes has a small thickness, its handling is difficult during the production process, resulting in cracking and breakage of capacitors, leading to a poor yield. When a garnet member has a small diameter, a central conductor assembly comprising the central conductors and the garnet member has a small inductance, necessitating the capacitors to have larger capacitance to operate at the same operation frequency, causing the same problems as the miniaturization of the capacitors. Though the garnet member having a larger thickness can increase the inductance of the central conductor assembly, it undesirably hinders the reduction of the thickness of an isolator. Further, the miniaturization of parts such as the capacitors and the garnet member results in the complicated structure of a box-shaped resin-conductor composite base, making it difficult to produce the resin-conductor composite base.
Because the isolator of Japanese Patent Laid-Open No. 9-55607 has a structure in which matching capacitors are formed inside the laminate module 105, it is considered that capacitance can easily be obtained by forming capacitors in a plurality of layers of the laminate module. The miniaturization of the laminate module is expected, because the above structure makes it easy to reduce an electrode area of a capacitor without reducing capacitance.
However, because the above isolator uses a laminate module 105 having an opening 110, the other ends of the central conductors 11a-11c are directly soldered to the lower case 92, and lower case-connecting electrodes (not shown) in the recess 114 on the lower surface of the laminate module 105 are soldered to the lower case 92. Because the lower case-connecting electrodes on the lower surface of the laminate module 105 are connected to ground terminals 108b, 108c, the other ends of the central conductors 11a-11c are grounded via the lower case 92 and lower case-connecting electrodes on the lower surface of the laminate module 105.
It is generally important that parts operable in a microwave frequency region such as isolators, etc. have internal circuits grounded without loss. In the case of the isolator, it is necessary that there is as little loss as possible in the lower case 92 and lower case-connecting electrodes on the lower surface of the laminate module 105 to ground the central conductor assembly 4 without loss. To suppress loss during the transmission of a high-frequency signal, the case is made of highly conductive materials such as silver, copper, etc., or it is provided with as thick plating or electrode as 30 xcexcm or more to reduce electric resistance. However, the lower case 92 is made of an iron-based metal, because it constitutes a magnetic yoke, thereby having a relatively low electric conductivity. Also, with as thick silver plating as 30 xcexcm or more, the case is as expensive as two times or more than otherwise.
Further, too thick plating tends to cause cracking in the plating layer due to internal stress, resulting in the deterioration of reliability. For instance, if gold is used instead of silver, gold forms a gold-rich alloy with solder components in a lead-tin solder, resulting in the formation of a mechanically brittle intermetallic compound, which leads to poor reliability. These problems indicate that it is difficult to obtain low-loss isolators with the structure of directly soldering central conductors to a lower case.
With respect to the lower case-connecting electrodes formed in a recess 114 on the lower surface of the laminate module 105, deformation is likely to occur in the laminate module with a large electrode thickness during the sintering process, due to the differences in a thermal expansion coefficient, a sintering shrinkage ratio, a sintering shrinkage speed, etc. between the dielectric materials such as ceramics and the electrode materials such as silver. Accordingly, the electrode cannot be made fully thick, resulting in poor electric conductivity in the lower case-connecting electrodes directly formed on the laminate module 105, making it difficult to ground the central conductors without loss. Thus, large loss cannot be avoided in the above isolator.
In the above isolator, external terminals 108a-108c are integrally formed on the bottom or side surfaces of the laminate module 105 for connection to a circuit board. It is considered that the laminate module 105 provided with external terminals is superior to a resin-conductor composite base provided with external terminals like the isolator as shown in FIG. 15, because of a smaller number of parts. However, when connection is kept between the external terminals formed on the laminate module 105 and an external circuit, stress would be concentrated on the external terminals of the isolator, if the parts-mounting circuit board forming the external circuit is deformed for some reasons, for instance, by dropping a mobile terminal, etc. Therefore, the laminate module 105 is easily broken, resulting in breakage of the isolator. Particularly when there is uneven surface flatness in the external terminals, they cannot be precisely positioned on a test plate for measurement of their characteristics, resulting in uneven measurement results. Thus, direct mounting of the external terminals to the laminate module tends to lower the reliability of the isolator.
Further in the above isolator, ridges 112 should be provided on both side ends on the lower surface of the laminate module 105 to provide the laminate module 105 with external terminals 108a-108c. In the production process of the laminate module 105, such integral steps make it impossible to press green sheets uniformly in a plane, leaving difference in density between the ridges and the recesses. This difference in press density leads to difference in a sintering shrinkage ratio between the ridges and the recesses, resulting in a deformed laminate module 105 after sintering. If the laminate module 105 is deformed, the external terminals have poor flatness, resulting in poor connection to the external circuit on the circuit board. Though a vertical load may be applied to the laminate module during sintering to suppress its deformation in a plane, this makes the sintering process complicated, undesirably increasing production cost.
Accordingly, an object of the present invention is to provide a miniaturized, low-loss, high-reliability, easy-to-produce non-reciprocal circuit device, and a wireless communications equipment comprising such a non-reciprocal circuit device.
The non-reciprocal circuit device of the present invention comprises a plurality of central conductors overlapping with electric insulation from each other at a predetermined angle, a magnetic body disposed in contact with or close to the central conductors, matching capacitors, a permanent magnet disposed for applying a DC magnetic field to the central conductors and the magnetic body, and metal cases for receiving these parts and serving as a magnetic yoke, at least the matching capacitors being integrally constituted in a laminate module having a substantially flat lower surface, and the laminate module being disposed on a substantially flat surface of a composite base comprising an insulation member and conductor plates.
Because the matching capacitors are formed in the laminate module in single or plural layers, the number of layers may be properly set to obtain the desired capacitance. Therefore, the capacitance of capacitors can be increased without increasing an electrode area. Because a reduced electrode area can be achieved with the same capacitance, the laminate module constituting capacitors can be miniaturized, resulting in miniaturization of an isolator. Further, by selecting materials having a small dielectric constant for the laminate module, the capacitors can be provided with reduced dielectric loss, thereby improving the loss characteristics of the isolator.
The laminate module having a flat lower surface is directly disposed on a flat upper surface of the composite base, a wide contact area can be obtained between both ground electrodes. Also, the composite base is disposed on the lower case, and the laminate module is disposed thereon, resulting in easiness in assembling of parts.
In a preferred embodiment, the composite base comprises a ground electrode connected to the central conductors and the capacitors of the laminate module and terminal electrodes connected to the central conductors and the capacitors of the laminate module on the same plane, the ground terminals connected to the ground electrode and the input/output terminals connected to the terminal electrodes being provided as external terminals on side surfaces and/or a lower surface of the laminate module. The laminate module has a ground electrode for connecting the capacitors to a ground on a substantially entire lower surface thereof, the ground electrode of the laminate module being disposed directly on a substantially entire upper surface of a ground electrode of the composite base and electrically connected thereto, and the ground electrode of the composite base being disposed directly on a lower metal case and electrically connected thereto.
With this structure, the lower surface of the laminate module is in close contact with the ground electrode (conductor plate) of the composite base and directly soldered to each other. The ground electrode (conductor plate) on a lower surface of the composite base is in close contact with the upper surface of the lower base and directly soldered to each other. Because this provides a wide contact area, the insertion loss is decreased, thereby providing good connection of the ground electrode and the terminal electrodes without loss. Further, it provides good characteristics of attenuating second and third harmonic, and improved mechanical strength. Thus, the close contact of the laminate module and the resin-conductor composite base to the lower case without gap is an important feature of the present invention.
With respect to external terminals such as the ground terminals connected to the ground electrode and the input/output terminals connected to the terminal electrodes, they are integrally formed on side surfaces and/or a lower surface of the composite base with a conductor plate, low loss can be achieved. Also, because the lower surface of the resin-conductor composite base is highly flat, insufficient contact is not likely with a test board or a parts-mounting circuit board, thereby providing a non-reciprocal circuit device with stable characteristics.
The composite base is desirably a resin-conductor composite base comprising conductor plates having an electric resistance of 5.5xc3x9710xe2x88x928 xcexa9xc2x7m or less integrally molded with an insulating thermoplastic resin. Though insulating materials forming the laminate module may be synthetic resins and ceramics, insulating thermoplastic resins such as polyethylene, polypropylene, polyethylene terephthalate (PET), etc. are preferable from the aspect of easy of production and impact resistance. Considering strength and heat resistance, it is preferable to use insulating thermoplastic engineering resins such as liquid-crystal, aromatic polymers containing silica fillers, polyphenylene sulfide, etc.
Though the conductor plate may be made of steel such as SPCC, copper, silver and other metals having the same low electric resistance preferable. Specifically, high-conductivity metals having electric resistance of 5.5xc3x9710xe2x88x928 xcexa9xc2x7m or less or metals plated with silver or copper are preferable. From the aspect of erosion of a circuit board with solder, a copper plate is preferable. From the aspect of formability, a metal plate of 0.03-0.15 mm in thickness is preferable.
With this structure, the insertion loss greatly lowers, and harmonic characteristics are remarkably improved. When the connection of the internal circuit of an isolator to an external circuit is carried out by the external terminals of the resin-conductor composite base, an external circuit board may be deformed for some external causes, for instance, by dropping of a cellular phone. In such a case, a stress that would otherwise be applied to the laminate module 5 would be absorbed by conductor plates of the external terminals and an insulating thermoplastic resin portion around the conductor plates in the resin-conductor composite base. Accordingly, the breakage of the laminate module and the isolator by stress can be avoided.
The terminal electrodes and at least one input/output terminal are integrally formed by the same conductor plate in the resin-conductor composite base. With this structure, an electric resistance can extremely be reduced between the terminal electrodes and the input/output terminals of the resin-conductor composite base, thereby remarkably suppressing electric loss in the connection of the central conductors and the capacitors to the external circuit.
A ground electrode and at least one ground terminal are preferably integrally formed by the same conductor plate in the resin-conductor composite base. With this structure, an electric resistance between the ground electrode and the ground terminals in the resin-conductor composite base can be made extremely low, thereby remarkably suppressing electric loss in the connection of the central conductors and the capacitors to a ground. This is an important feature of the present invention, because the connection of the internal circuit to a ground without loss is important for the reduction of loss in parts operable in a microwave region such as an isolator, etc.
The ground electrode and the terminal electrodes of the resin-conductor composite base preferably have contact surfaces in the same plane. With this structure, the laminate module has input/output electrodes connected to the terminals of the resin-conductor composite base and a ground electrode connected to the ground electrode of the resin-conductor composite base in the same plane on a surface in contact with the resin-conductor composite base. This makes it unnecessary to provide the laminate module with ridges necessary for the conventional non-reciprocal circuit device shown in FIG. 16, thereby avoiding the deformation of the laminate module without complicated production processes.
The resin-conductor composite base preferably has a means for positioning the laminate module on a flat upper surface thereof. Utilizable as a positioning means is, for instance, external terminals provided on side surfaces of the resin-conductor composite base. This structure facilitates the mounting, positioning and fixing of the laminate module onto a flat surface of the resin-conductor composite base, resulting in the simplification of production processes. Further, because improper positioning of the laminate module relative to the resin-conductor composite base can be suppressed, the production yield of the non-reciprocal circuit device is improved.
The central conductors are preferably formed in an integral central conductor laminate comprising a plurality of ceramic sheets having central conductor patterns. The ceramic sheets are preferably formed of magnetic ceramics such as garnet. This structure makes it possible to form the capacitors and the central conductors into an integral laminate, thereby achieving the miniaturization of the non-reciprocal circuit device, the simplification of its structure, and thus shortening the production processes. Also, to obtain high dimension accuracy and stable electric characteristics, it is effective to use a central conductor assembly comprising central conductors formed from a copper plate by etching, which are wound around a microwave magnetic, sintered ferrite member at a predetermined angle.
The electrode patterns in the laminate module are preferably connected through via-electrodes and/or side-surface electrodes. Also, the electrode patterns in the central conductor laminate are preferably connected through via-electrodes and/or side-surface electrodes. With via-electrodes, the number of production can be reduced to lower the production cost of the non-reciprocal circuit device, though they are slightly disadvantageous in miniaturization. In the case of using electrodes printed on side surfaces, the non-reciprocal circuit device can be further miniaturized. Using both via-electrodes and electrodes printed on side surfaces, the resistance of conductors can be suppressed while compensating defects of both electrodes, thereby achieving low loss.
The central conductors are preferably bent along an outer surface of the magnetic body, and insulation films are disposed between the central conductors in their crossing portions. The central conductors and the magnetic body are formed by an integral laminate comprising a plurality of ceramic sheets having central conductor patterns.
In the preferred embodiment, at least a lower case of the metal cases is formed by an integral laminate of a metal having as high saturation magnetic flux density as 0.6 T or more clad with a high-conductivity metal having an electric resistance of 5.5=10xe2x88x928 xcexa9xc2x7m or less, whereby the lower case serves as an electrically conductive magnetic yoke.
The wireless communications equipment of the present invention comprises the above non-reciprocal circuit device, a transmission circuit, a reception circuit, and an antenna. The wireless communications equipment is preferably a cellular phone.